For many years flexible catheters have been used to place various devices within the vessels of the human body. Such devices include dilatation balloons, radio-opaque fluids, liquid medications and various types of occlusion devices such as balloons and embolic coils. Examples of such catheter devices are disclosed in U.S. Pat. No. 5,108,407, entitled “Method And Apparatus For Placement Of An Embolic Coil”; U.S. Pat. No. 5,122,136, entitled, “Endovascular Electrolytically Detachable Guidewire Tip For The Electroformation Of Thrombus In Arteries, Veins, Aneurysms, Vascular Malformations And Arteriovenous Fistulas.” These patents disclose devices for delivering embolic coils to preselected positions within vessels of the human body in order to treat aneurysms, or alternatively, to occlude the blood vessel at the particular location.
Coils which are placed in vessels may take the form of helically wound coils, or alternatively, may be random wound coils, coils wound within other coils or many other such configurations. Examples of various coil configurations are disclosed in U.S. Pat. No. 5,334,210, entitled, “Vascular Occlusion Assembly; U.S. Pat. No. 5,382,259, entitled, “Vasoocclusion Coil With Attached Tubular Woven Or Braided Fibrous Coverings.” Embolic coils are generally formed of radiopaque metallic materials, such as platinum, gold, tungsten, or alloys of these metals. Often times, several coils are placed at a given location in order to occlude the flow of blood through the vessel by promoting thrombus formation at the particular location.
In the past, embolic coils have been placed within the distal end of the catheter. When the distal end of the catheter is properly positioned the coil may then be pushed out of the end of the catheter with, for example, a guidewire to release the coil at the desired location. This procedure of placement of the embolic coil is conducted under fluoroscopic visualization such that the movement of the coil through the vasculature of the body may be monitored and the coil may be placed at the desired location. With these placements systems there is very little control over the exact placement of the coil since the coil may be ejected to a position some distance beyond the end of the catheter.
Numerous procedures have been developed to enable more accurate positioning of coils within a vessel. Still another such procedure involves the use of a glue, or solder, for attaching the embolic coil to a guidewire which, is in turn, placed within a flexible catheter for positioning the coil within the vessel at a preselected position. Once the coil is at the desired position, the coil is restrained by the catheter and the guidewire is pulled from the proximal end of the catheter to thereby cause the coil to become detached from the guidewire and released from the catheter system. Such a coil positioning system is disclosed in U.S. Pat. No. 5,263,964, entitled, “Coaxial Traction Detachment Apparatus And Method.”
Another coil positioning system utilizes a catheter having a socket at the distal end of the catheter for retaining a ball which is bonded to the proximal end of the coil. The ball, which is larger in diameter than the outside diameter of the coil, is placed in a socket within the lumen at the distal end of the catheter and the catheter is then moved into a vessel in order to place the coil at a desired position. Once the position is reached, a pusher wire with a piston at the end thereof is pushed distally from the proximal end of the catheter to thereby push the ball out of the socket in order to release the coil at the desired position. Such a system is disclosed in U.S. Pat. No. 5,350,397, entitled, “Axially Detachable Embolic Coil Assembly.” One problem with this type of coil placement system which utilizes a pusher wire which extends through the entire length of the catheter and which is sufficiently stiff to push an attachment ball out of engagement with the socket at the distal end of the catheter is that the pusher wire inherently causes the catheter to be very stiff with the result that it is very difficult to guide the catheter through the vasculature of the body.
Yet another coil deployment system is disclosed in U.S. Pat. No. 5,261,916, entitled, “Detachable Pusher-Vasooclusive Coil Assembly with Interlocking Ball and Keyway Coupling.” This system includes a pusher member with a tubular portion at its distal end that has a keyway for receiving the enlarged bead of an embolic coil through the outer wall and into the lumen of the tubular portion. The enlarged bead of the coil is positioned within the keyway and a resilient wire coupling the bead to the coil extends axially over the outer diameter of the distal end of the tubular portion to the remaining portion of the coil. The enlarged bead is retained in the keyway, forming an interlocking arrangement, by positioning the assembly within the lumen of an outer sleeve. Once the keyway is pushed from the confines of the sleeve the bead can disengage from the keyway. With this system the inner diameter has to be sufficiently large to accommodate the stack up of the wire coupled to the bead and the diameter of the tubular portion. Also when placing coils in an aneurysm “packed” with coils, there may not be enough room for the enlarged bead to disengage from the keyway.
Another coil release system is disclosed in U.S. Pat. No. 5,895,391 to Farnholtz, entitled, “Ball Lock Joint and Introducer for Vaso-occlusive Member”. This system incorporates a tubular member having a portion of the wall cut away to receive at least a portion of an enlarged bead coupled to the proximal end of the embolic coil. A wire is placed within the lumen of the tubular member and cooperates to form an interference fit between the wire, bead and cut-away wall portion. To release the coil, the wire is pulled from the proximal end of the system to remove the interference fit with the bead and cut-away wall portion.
Still another coil deployment system utilizes a pair of jaws placed on the distal end of a pusher wire to position and release a coil. One such system is described in U.S. Pat. Nos. 5,601,600 and 5,746,769 to Ton et al., entitled, “Endoluminal Coil Delivery System Having A Mechanical Release Mechanism.” Ton discloses an elongate pusher wire having jaws at the distal end. The jaws include tip projections which are perpendicular to the longitudinal axis of the pusher wire and when positioned with the lumen of a collar fixed to the proximal end of a coil, interlockingly engage with matching detents placed in the wall of the collar. A tubular body is used to slide over the pusher wire to collapse the jaws and release the collar. The disclosed interlocking engagement between the jaws and collar prevents forward and backwards axial movement of the jaws relative to the collar and allows any torqueing force applied to the jaws to be translated to the collar and affixed coil. Transmission of torque from a coil delivery system to a coil during the treatment of aneurysm may be detrimental to precise placement of the coil. The coils may coils store the torque energy and upon release from the delivery system, release the stored energy causing the coils to move unpredictably. Ton also states that jaws may be fixed to the coil, but does not provide or disclose any information as to how this may be accomplished.
Another method for placing an embolic coil is that of utilizing a heat releasable adhesive bond for retaining the coil at the distal end of the catheter. One such system uses laser energy which is transmitted through a fiber optic cable in order to apply heat to the adhesive bond in order to release the coil from the end of the catheter. Such a method is disclosed in U.S. Pat. No. 5,108,407, entitled, “Method And Apparatus For Placement Of An Embolic Coil.” Such a system also suffers from the problem of having a separate, relatively stiff element which extends throughout the length of the catheter with resulting stiffness of the catheter.
Another method for placing an embolic coil is that of utilizing a heat responsive coupling member which bonds the coil to the distal end of a delivery system. One such system uses electrical energy which is transmitted through electrical conductors to create heat which is applied to the coupling member to thereby soften and yield the coupling member in order to release the coil from the end of the delivery system. Such a method is disclosed in U.S. Pat. No. 7,179,276, entitled, “Heated Vascular Occlusion Coil Deployment System.” Such a system suffers from the problem of having to pull an engagement member once the coupling is softened in order to release the coil.